Refilling sealed hot-water system


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Old 09-15-04, 05:37 PM
jlar310
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Question Refilling sealed hot-water system

My sealed hot water system has a manual fill-valve. The expansion tank is in the floor joists just above the boiler. The tank has no gauges or windows to check the level.

Before draining, I noted the pressure on the (cold) boiler -- 20 psi. I refilled and bled the radiators until I was again at 20 psi with no air. But what about the tank? How does that fit into the equation? As I understand, it should have some air in it to allow for expansion of the water at operating temperature, but how do I know without a gauge? Should I just close the inlet valve to the tank and drain out all or some of the water, then reopen the inlet?

Also, I'm new to this-old-house. How do I know what the pressure in the system really should be? The gas-fired bolier is rated at max 100 psi. The T&P valve is rated at 30 psi.
 
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Old 09-16-04, 07:02 PM
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The only way to reset the amount of air in the open expansion tank is to drain ALL the water out and refill it. Never drain out just part of the water or you will create a problem you may not have had before.

As far as system pressure goes, 12-15 psi is usually plenty. It has to do with the height of the highest radiator above the boiler. It takes about 1 pound of water pressure to lift water 2 feet.

Ken
 
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Old 09-16-04, 07:57 PM
jlar310
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So, if I'm reading you right, I need to open the drain valve on the expansion tank, drain it completely to allow it to refill with air via the drain valve. Then close the tank drain valve and add more water to the system to bring it back up to pressure. Right?
 
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Old 09-17-04, 04:59 AM
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You are correct. The only thing I failed to mention is that you should have a valve there to isolate the tank from the heating system during the draining so you don't take any water out of the heating system.

Ken
 
 

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